1. Field
The following description relates to a Passive Optical Network (PON), and more particularly, to a link setup method in a Wavelength Division Multiplexing Passive Optical Network (WDM PON) system.
2. Description of the Related Art
In response to the development of optical communication technology and a sharp increase in the demand of Internet services, basic research on an optical subscriber network has been conducted since the early 2000s, and currently the introduction of a broadband subscriber network, such as Fiber To The Home (FTTH) and Fiber To The Office (FTTO), which connects a remote station or a central office (CO) with a subscriber through an optical fiber, is actively in progress. Recently, research on technology for the next-generation, high-speed, high-capacity optical subscriber network has been actively carried out in response to the phenomenal traffic growth due to the proliferation of mobile Internet protocol (IP) terminals, such as a smart phone and a tablet computer, the commercialization of IPTV services, and the spread of multimedia broadcasting/streaming services over the Internet.
The methods used for efficiently providing a service to as many subscribers as possible using a limited amount of network resources are Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM) schemes, and, in recent years, many attempts have been made to integrate various schemes for mobile communications, such as Orthogonal Frequency Division Multiplexing (OFDM), to optical subscriber network technology. A WDM scheme which assigns a unique wavelength to each subscriber for communications can provide the individual subscribers with high-speed communication services, as well as easily increase communication capacity and a number of subscribers and also have excellent communication security. Thus, more attention is paid to a hybrid WDM scheme for the next-generation high-speed, high-capacity optical subscriber network technology.
In a Wavelength Division Multiplexing Passive Optical Network (WDM PON), data transmission/reception between each subscriber and a central office (CO) is performed using a unique wavelength assigned to the each subscriber. Basically, a WDM PON system includes a service providing device (hereinafter, referred to as an “optical line terminal (OLT)”) at a CO side, a user terminal device or a plurality of subscriber devices (hereinafter, referred to as optical network units (ONUs)) around the user terminal device, and a local node or optical distribution network (ODN) in which one or more optical multiplexers/demultiplexers (Mux/Demux) or optical intensity splitters are placed. A network configuration may vary depending on a type of light source, for example, a spectrum-sliced light source, a wavelength-locked light source, or a wavelength-independent light source. Other types of hybrid WDM scheme may have different network configurations.
Wavelength assignment to ONUs is prerequisite to link setup for communications between the OLT and each ONU in a WDM PON system. The procedures for link setup between OLT and ONUs, including the wavelength assignment, may differ according to the network configuration which may vary depending on the type of a light source and/or whether the system is a hybrid type or not. Since elements or devices for use in establishing the WDM-PON system are not compatible with each other, the change of the wavelength assignment process according to the network configuration may lead to an increase of price. Furthermore, the link setup process that differs depending on the network configuration may hinder the development of hybrid WDM schemes.